Self Assessment
SA1 Form: How to Register for Self Assessment
The SA1 is the form used to register for Self Assessment. Most people can register online, and you must do it by 5 October after the end of the tax year in which you first need to file.
Last reviewed 10 November 2026 · Written by the Right Choice Consulting team
What is the SA1 form?
The SA1 is the paper form for registering for Self Assessment as an individual. After registering, HMRC issues a Unique Taxpayer Reference (UTR), a 10-digit number you need to file returns.
Who needs to register?
- Sole traders with income above the reporting thresholds.
- Landlords with rental income.
- Partners in a partnership.
- Directors or others with untaxed income HMRC cannot collect through PAYE.
Deadlines
You must register by 5 October following the end of the tax year in which you started the activity or received the income. Your first return is then due by 31 January the following year.
How to register
- Register online through GOV.UK where available, or use the SA1 form.
- Provide your details and the type of income.
- Wait for your UTR and activation code to arrive by post.
- Activate your online account to file your return.
Do you need an SA1 if you already have a UTR?
If you have filed before, you generally already have a UTR and do not need to register again, though you may need to tell HMRC about a new source of income.
Sources
This article is general information based on UK rules as understood at the review date above. It is not personal tax or legal advice. Rates, thresholds and rules change; confirm the position for your situation with an accountant or on GOV.UK.